The term "Sinister" and "Dexter" occasionally appear in texts of classical astrology and provide a more careful description of the working of an aspect formed between two planets, or cast from a planet to an angle. The rules add to a more accurate chart interpretation, but unfortunately the subject has been due to much confusion and error, as can be seen in many textbooks. Therefore, a correct explanation has been badly in need.

A Sinister aspect is performed when a swifter planet applies to an aspect cast ahead of itself in the zodiac. A Dexter aspect is formed then the applying planet casts its aspect backwards, against the flow of the signs. The sinister or dexter aspect involves both of those planets that are in aspect. Take the example of Mercury in 6 Aries and Mars in 6 Leo; if Mars is the significator, then Mars will receive the sinister trine form Mercury; if Mercury is the significator, then he will form a sinister trine to Mars. The applying planet tells who is initiation or moving into the event.

A sinister aspect is a left-handed aspect. A dexter aspect is right-handed. To keep difference in what is left and right, think of it in point of the Sun facing the Earth - and which side then lies to the Suns left and right. The left side lies ahead of the Sun in an earlier sign in consideration of the flow of the zodiac. The natural motion of the planets is with the zodiac and facing Earth (not with their backs turned as the inferior planets appear during their inferior conjunction with the Sun). So a sinister aspect is the tightening of celestial muscles and delivery of a punch from the celestial left; a dexter aspect from the celestial right.

Dexter

When an aspect is dexter is just like a right-hand punch; full of force and major impact. The action is clear and deliberate, making an obvious case. The marks are there. Whatever the aspects signifies will be evident in a most determined, decisive and pronounced manner. With the dexter aspect there is both intent and delivery.

Sinister

A sinister aspect is like a left-foot kick at goal. It is weaker and with reduced force. The significator has less command of the situation and the ball may not meet its target. The querent could be in the dark and unaware the state of affairs. Sinister aspects do not always live up to expectations. The outcome depends upon a matter of touch. Parties may lack concentration and accident brings about the outfall. However, sometimes the event will creep up and spring into the open through the agency of an unexpected turn. Left foot kicks take you by surprise. The nature of the planets involved must be studied to determine whether the effects will be good or bad. Perhaps the sinister aspect indicates a risk or gamble, or matters are approached from either the wrong or least likely angle. On a statistical basis there is less likelihood of their effects working out.

Aspects

The dexter square is most forceful; the sinister square is less evil, since it doesn't have the same kick. A dexter trine is of full fortitude, but the sinister trine is like an uncertain promise. The dexter sextile is good, but the sinister sextile does not possess the same force of action and may even be the cause of irritation. Not withstanding, in all cases of judgment observe whether the planet is a fortune or infortune and whether it be in a good celestial state; if the planet is in a good condition and possesses dignities in the place to which he does apply, he will still perform the sought effects. Planets that have essential dignity perform; those who do not fail in bringing any good, the good does not last or matters collapse.

Example charts

On p155 of Christian Astrology, Lilly gives and example where Venus, Lady of the Ascendant, is in Gemini and applies by sinister trine to the Ascendant and to Jupiter, who is in Libra in the first house. He says that had this been the moment of a sudden accident, it could not have redounded to the querents disadvantage, but done rather good.

On p165 of CA, regarding a ship at sea, the Moon in Virgo casts her sinister square to Fortuna in Sagittarius (but both below the horizon), and Mercury cast his dexter square from Pisces to Fortuna; there was no doubt that the ship was cast away.

On p393 of CA, the application of Sol in Virgo by trine dexter to Saturn in Taurus, who is lord of the Capricorn Ascendant; the missing dog was brought back to the querent on the very day of the aspects perfection.

On p396 of CA, Mars makes a dexter square to Mercury who is significator of a thief. Mercury is stationary and Mars would not form a dexter square to Mercury if he were not slow. The dexter square, Mars applying to Mercury, gives the thief scars in his face.

Page 402 of CA says Lilly: "That according to natural causes in Art, the Enemy should be worsted, I had these reasons; first because Saturn the Lord Hoptons significator is sub radis (under beams); next, he is in his Fall; thirdly beholding no aspect of any Planet, but wholly peregrine and unfortunate, beholding the cusp of the seventh with a square dexter (from Aries to Capricorn), arguing loss to his Army, and dishonor to himself by the fight, &c.

Addition 03. July 2004

The dexter aspect is like the safe move of a football team where the ball is kept in possession and played backwards into ones own team and field, with the intention of gaining the support and follow-through of fellow players. This allows the team to fortify the attack by means of a more steady and determinate build-up. The sinister aspect is more like booting the ball up field in the stray search of an attacker. The sinister aspect moves the ball into foreign/ unknown ground - and the move may thus be termed more bold, daring, reckless and adventurous.

In rugby the ball may be thrown backwards into the home field to a player of the same team, but only kicked forwards. OR the player may win his team a point by out-running, or running through the hazard of the opposing defence while in possession of the ball.

The dexter is a safe-return, while the sinister is like a counter attack or at its best a shrewd attack when both skill, balance and the element of surprise are all present. With the sinister aspect someone is caught off-balance. If the planet is in a good condition and possesses dignities in the position to which he does apply - perfection will follow.

Addition 24. September 2006

The sinister sextile through signs of long ascension is most likely to create a sudden burst of optimism and confidence, but causing an advance that fails and that soon may be counteracted. It would be like a spontaneous attack in football that misses its aim, puts the ball in the place of the opponent and causes an unexpected turn in the game. In financial markets early rallies may lead to reversals.

The sinister square through signs of long ascension has more than any other aspect the capacity to bring about a bold move, which succeeds through the element of surprise and brings about an experience of talent combined with fluke luck.

The sinister trine through signs of short ascension is probably the most dangerous aspects where disaster may be the end result of error or neglect. With this aspect the quesitive is apt to failure and there is every need to double-check and stay on ones toes, as it were. In the case of the "Aviation disaster at Torghatten" the plane was out of course.

The sinister square through signs of short ascension is likely to bring things safe and home, and may be though the act of heroism.

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The dexter sextile though signs of long ascension indicate a defensive move or routine, but one that may lead to expense and delay rather than fortune. Tradition does not work out and there may be the case of unfortunating ones objective. There may be the case of poor judgment or getting lost. As example, in the financial markets where one might to sell a position to secure a profit - and attempt to recapture it at a more reasonable price later, but this does not occur - the end result being both addition cost and the loss of a valuable position in the market. 

The dexter square through signs of long ascension is where talent and skill converts to a calculated and desirable fortitude. Matter is worth working with and a good days work is delivered. Efforts lead to credit, pride and remuneration. 

The dexter trine through signs of short ascension shows neglect, error or maybe even sabotage. There may be an abuse of wealth, trust or position. The aspect is likely to be evil in effect and more forceful than the sinister trine. Someone's due to a major sucking up. Fraud is about, or a trickster, and the party may be suspected of knowing what he's up to.  The aspect is warning to refrain from acting.